This is a continuation application of U.S. application Ser. No. 09/934,681, filed Aug. 23, 2001 now U.S. Pat. No. 6,721,389, which in turn claims priority from European Patent Application Nos. 00202960.1, filed Aug. 25, 2000, and 01302647.1, filed Mar. 22, 2001, the entire contents of which are hereby incorporated by reference.